Polymer deposition and modification of membranes for fouling resistance

ABSTRACT

The present invention describes methods and compositions for the reduction, prevention and elimination of biofilm formation on a surface. The present invention provides a method of depositing a coating material to reduce or prevent biofilm formation on a surface by adding a dopamine coating material to a liquid solvent to form a solution mixture, adjusting a pH of the solution mixture to 8, 9, or 10 and dissolving the dopamine coating material in the liquid solvent. The solution mixture is then placed into contact with one or more surfaces to form a dopamine coating on the surface to reduce biofilm formation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. Provisional Application Ser. No. 61/079,608, filed Jul. 10, 2008, the contents of each of which are incorporated by reference herein in their entireties.

STATEMENT OF FEDERALLY FUNDED RESEARCH

This invention was made with U.S. Government support under National Science Foundation Agreement numbers DMR-0423914 and 0650277. The government has certain rights in this invention.

TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to the field of membranes for water purification, and more particularly to the deposition of polymers and modification of membrane surfaces to reduce biofilm formation on membranes.

INCORPORATION-BY-REFERENCE OF MATERIALS FILED ON COMPACT DISC

None.

BACKGROUND OF THE INVENTION

Without limiting the scope of the invention, its background is described in connection with the use of hydrophilic polymers to coat and modify membrane surfaces to reduce membrane fouling, scaling and/or biofouling, specifically reducing biofilm formation, salt crystallization on a membrane's surface, or the accumulation of other foulants (e.g., natural organic matter, colloidal matter, emulsified oil droplets, and other types of foulants that may be found in feed streams of interest).

One of the major problems with membrane water purification is fouling of the membrane. Generally, fouling occurs when impurities in water deposit on the surface of the membrane and is also seen when the internal pore structure of the membrane is obstructed. Biofouling is a subset of fouling where bacterial colonies undergo proliferation and deposition on the membrane. The bacteria, in turn, form biofilms with significant mass transfer resistance through bacterial secretion of extracellular polymeric substances on the membrane surface and, if the membranes are porous, into the membrane pore structure.

Biofilms are remarkably difficult to treat with antimicrobials. In some cases the antimicrobial compositions may be readily inactivated or fail to penetrate into the biofilm. Furthermore, the microorganisms distributed throughout the biofilm may be from different geographic locales and the same species microorganisms may have different characteristics depending on the geographical location in the biofilm. Biofilms are often comprised of a variety of different species which may offer protection to one another. Microorganisms may also express new, and sometimes more virulent phenotypes when grown within a biofilm, allowing for alterations in colony morphology, metabolism, and growth rate in the sessile state to improve microbial resistance. For example, microorganisms within the biofilm may have an increased (e.g., up to 1000-fold higher) resistance to antimicrobial compounds, even though these same microorganisms are sensitive to these agents if grown under planktonic conditions. Such phenotypes may not have been detected in the past because the organisms were grown on rich nutrient media under planktonic conditions. The growth conditions are quite different, particularly in the depths of biofilms, where nutrients and oxygen are usually limited, and waste products from neighbors can be toxic. In short, microorganisms found at the bottom of the biofilm look and act differently from microorganisms located at the surface.

Another major problem with membrane water purification is scaling of the membrane. Generally, scaling occurs when partially soluble salts deposit on the membrane as a result of their concentration rising above their solubility limit near the membrane surface. The deposition of these contaminants can lead to a dramatic reduction in water flux, which increases operating costs and decreases membrane lifetime.

There have been many studies that have addressed membrane surface modification to alleviate membrane fouling. However, these studies mainly focused on grafting or coating hydrophilic molecules to a specific support membrane. Many of these techniques are not applicable to multiple types of water purification membranes and many require commercially unviable treatment steps, such as plasma treatment.

For example, United States Patent Publication Number 2006/0009550 teaches a surface modification method involving the addition of a polymerization initiator composition comprising a dihydroxyphenyl terminated halide, followed by reaction with a monomer to form a surface bound polymer. The modified surfaces have a variety of medical and industrial applications involving prevention of cell and protein adhesion on medical devices and other surfaces. These modified surfaces are used to control and prevent algal and bacterial growth on water lines used for industrial and drinking water.

United States Patent Publication Number 2008/0149566 discloses a method of coating a surface with a multifunctional biocoating by contacting a portion of a substrate with an alkaline solution of a surface modifying agent (SMA) like dopamine so as to introduce reactive groups on the surface. Furthermore, the application teaches a method for adding a secondary reactive moiety to the SMA treated surface to yield modified substrates with specific functionalities.

SUMMARY OF THE INVENTION

The present invention provides methods and compositions to alleviate fouling, scaling, and/or biofilm formation (i.e., biofouling) of conventional polymeric membranes using a novel polymer deposition. The present invention provides a highly hydrophilic polymer, polydopamine, which can be deposited with strong adhesion onto virtually any surface. In addition, the present invention provides a substrate for the attachment (covalently and/or non-covalently) of molecules to provide specific membrane surface chemistries and properties. The present invention also provides a highly hydrophilic polymer that can further react with metal ions to form metallic particles on the membrane surface via an electroless metallization mechanism.

The present invention provides methods and compositions to alleviate biofilm formation on membranes using hydrophilic molecule attachment (such as poly(ethylene glycol)); attachment of metal ions (e.g., silver/copper) to polydopamine; and attachment of other molecules to the membrane surface (e.g., furanones can reduce bacterial proliferation on surfaces). The present invention also provides methods and compositions to alleviate fouling and/or scaling by tuning pertinent membrane surface properties through the attachment of long chain polymers (e.g., poly(ethylene glycol) (PEG) and other hydrophilic or hydrophobic polymers) to the polydopamine deposition layer.

The polydopamine of the present invention increases the membrane resistance to biofilm formation, fouling and/or scaling, which, in turn, results in higher membrane fluxes. Furthermore, the present invention may be tailored to specific properties through the addition of compositions from a library of possible compounds available to covalently attach to the polydopamine layer, making it an extremely versatile modification.

The present invention also provides a method for treating and/or coating existing surfaces or membrane support through non-specific adhesion of polydopamine to any surface, therefore allowing modification of all wetted parts of a membrane module or membrane treatment system. Another advantage of the polydopamine deposition of the present invention is its ease of applicability to membrane modules and other wetted parts of membrane treatment systems, even in large-scale applications. In addition, all the wetted module parts that are susceptible to fouling can be modified by the present invention. Furthermore, polydopamine is applicable to practically any membrane, regardless of membrane material, whereas most surface modification techniques have only been accomplished using one specific membrane. Polydopamine can also react with many different conjugated molecules, which allows membrane surface properties to be further tuned to specific applications.

The deposition process occurs by simply dissolving dopamine in an alkaline water solution (e.g., 8-14 pH) and circulating the dopamine solution through a membrane module housing for a period of time (e.g., 30 minutes). In contrast to the present invention, most membranes surface modification result in a dramatic pure water flux loss, due to the polymer layer increasing the membrane's overall mass transfer resistance. The polydopamine-coated membranes of the present invention lose relatively little pure water flux when compared to uncoated membranes, as the polydopamine coating layer is extremely thin, e.g., polydopamine coating layers as thin as approximately 5 nm are possible on polysulfone, a common polymer for ultrafiltration membranes.

The coating of polydopamine to a membrane surface relies on an oxidation reaction to convert dopamine to polydopamine that takes a significant amount of time. The deposition is a somewhat slow process. Most anti-fouling experiments attempted have used membranes that have been immersed in dopamine solution for 30-90 minutes. Although this is not exceedingly long, for industrial practicality, shorter and longer immersion times may also be optimal depending on the specific application.

The present invention provides a method of depositing a coating material to reduce or prevent fouling, scaling, and/or biofilm formation on a surface by adding a dopamine coating material to a liquid solvent to form a solution mixture, adjusting the pH of the solution mixture to an alkaline pH (e.g., 8, 9, or 10) and dissolving the dopamine coating material in the liquid solvent. The solution mixture is then placed into contact with one or more surfaces to form a dopamine coating on the surface to reduce fouling, scaling, or biofilm formation.

The dopamine coating may form a polydopamine coating and in addition may include one or more polymers, one or more polar sugars, one or more polar salts, one or more polar organic molecules, one or more polar —OH containing molecules, one or more polar —NH₂ containing molecules, one or more —SH containing molecules, one or more halide-containing molecules, one or more polar O containing molecules, one or more polar molecules, one or more polar hydrophilic molecules, one or more molecules comprising at least one polar group or combinations thereof. The dopamine coating may include one or more silver, zinc, copper, metal ions, alloy ions, nanoparticles, metal nanoparticles, inorganic molecules or combinations thereof.

The present invention includes a liquid separation apparatus having reduced fouling, scaling, and/or biofilm formation including a purification membrane and a polydopamine layer deposited on the purification membrane to form a polydopamine coated membrane to reduce fouling, scaling, and/or biofilm formation, wherein the polydopamine layer increases the hydrophilicity of the purification membrane and the polydopamine coated membrane has high water flux. One or more containers are positioned on different sides of the polydopamine coated membrane to contain the separated liquid.

The present invention also includes a polydopamine coated purification membrane system for modification of conventional purification membranes to reduce fouling, scaling, and/or biofilm formation having a dopamine solution disposed in a feed tank, a pump connected to the feed tank to move the dopamine solution, a membrane inlet connection connected to the pump to a membrane that allows the dopamine solution to be deposited on the membrane, and a membrane outlet connection to connect the membrane to the feed tank to return the dopamine solution to the feed tank.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures and in which:

FIG. 1 is a schematic of the structure of dopamine and assumed structure of polydopamine;

FIG. 2 is a plot of the pure water permeance of an ultrafiltration (UF) polysulfone membrane modified with different polydopamine deposition times and polydopamine deposition thickness on a Udel polysulfone thin film as measured by ellipsometry;

FIGS. 3A, 3B, 3C, 3D, 3E, 3F, and 3G are graphs of non-ionic oil emulsion fouling studies on various polydopamine and PEG modified and unmodified microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) membranes. The results for an unmodified membrane are labeled “Unmodified” in this figure. Results from membranes modified with polydopamine alone are labeled “PDOPA”, and results from membranes modified with dopamine and subsequently also modified with poly(ethylene glycol) (PEG) are labeled “PDOPA-g-PEG”. Rejection values given in the figures for MF and UF membranes are total organic rejection at the end of each fouling trial, and rejection values for NF and RO membranes are total salt rejection at the end of each fouling trial. FIG. 3 h presents dodecyl trimethylammonium bromide and decane emulsion fouling for modified and unmodified RO membranes;

FIG. 4 is a plot comparing pure water flux through nascent (unfouled) and fouled (after rinsing) polydopamine and PEG modified and unmodified MF, UF, NF, and RO membranes;

FIG. 5 is a graph of the adhesion of Pseudomonas aeruginosa to modified and unmodified membranes as measured by the luminescent intensity of genetically modified Pseudomonas aeruginosa.

FIG. 6 illustrates a crossflow system having a feed tank connected to membrane cells; and

FIG. 7 is a schematic of a modified crossflow system for polydopamine deposition and subsequent PEG adhesion.

DETAILED DESCRIPTION OF THE INVENTION

While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention.

To facilitate the understanding of this invention, a number of terms are defined below. Terms defined herein have meanings as commonly understood by a person of ordinary skill in the areas relevant to the present invention. Terms such as “a”, “an” and “the” are not intended to refer to only a singular entity, but include the general class of which a specific example may be used for illustration. The terminology herein is used to describe specific embodiments of the invention, but their usage does not delimit the invention, except as outlined in the claims.

As used herein the term “molecule” is used to refer to a combination of two or more atoms in a definite arrangement held together by covalent chemical bonds and is generally considered the smallest particle of a pure substance that still retains its composition and chemical properties.

As used herein the term “water flux” or “flux” is used to refer to the volume of solution (e.g., water, clean water, permeate solution, etc.) flowing through a given membrane area during a given time. Measurement of the amount of water or permeate solution that flows through a membrane.

In general, bacterial biofilms are organized, sessile collections of microorganisms that commonly develop on water purification, wastewater treatment, and bioreactor membranes and reduce flux and compromise rejection properties.

Biofilm growth provides a number of advantages to its constituent organisms over growth in the planktonic state, including enhanced nutrient access, improved antimicrobial resistance, and synergistic associations with other nearby cells. The biofilm is initiated by a conditioning film forms on the substrate surface, usually comprised of proteins and other organic matter. Bacteria are brought close to the surface by fluid flow where they can adhere (reversibly and irreversibly) to the conditioned surface. The microorganisms grow and divide, colonizing the surface and producing large quantities of sticky extracellular matrix polymers, until they undergo detachment to the planktonic state to colonize at other locales. Naturally-occurring biofilms are a poorly-understood complex of many bacterial species. One example is Pseudomonas aeruginosa, a gram-negative, rod-shaped organism that can be found in nearly all natural waters, including drinking reserves and widely known to prolifically foul surfaces, forming robust biofilms due to its rapid rate of reproduction. In addition, Pseudomonas aeruginosa is an opportunistic human pathogen, responsible for biofilm formation in medical devices and infections of many hospital patients, especially those suffering from burn wounds and cystic fibrosis. In the art, biofilm formation is typically addressed with feedwater chlorination (e.g., in water purification) and mechanical cleaning/backwashing of the membrane (e.g., both water purification and membrane bioreactor systems). If conditioning film formation and bacterial adhesion can be reduced, fouling biofilms should be slower to develop on membranes.

The present invention provides a polydopamine deposition on a variety of surfaces and allows surface modification of a variety of membranes, regardless of membrane material, e.g., microfiltration: polypropylene, poly(vinylidene fluoride), poly(tetrafluoroethylene), ultrafiltration: polysulfone, poly(ether sulfone), nanofiltration: polyamide and reverse osmosis: polyamide. These surfaces were examined for their effectiveness against Pseudomonas aeruginosa attachment.

The present inventors recognize that modified or substituted dopamine can be used to form a substituted polydopamine on the membrane surface. The substitution may be one or more lower alkyl groups, alkenyl groups, amino groups, aryl groups, alkylaryl groups, halogen groups, halo groups, haloalkyl groups, phosphoryl groups or combination thereof. The substituted polydopamine may have one or more groups and the groups may be similar or different groups. In addition, the individual monomer, copolymers, subunits or polymers may be substituted with one or more molecules, groups or atoms. The number, position, location and type of modification may be varied by the skilled artisan. The modifications may include the addition of one or more of the following groups: lower alkyl, alkenyl, amino, aryl, alkylaryl, halogen, halo, haloalkyl, phosphoryl or combination thereof.

The present invention includes a deposition method used to treat membranes with dopamine to form polydopamine on the membrane surface and in the case of porous membranes, inside the membrane pores. This method is advantageous over other modifications because of its ease of applicability to virtually any membrane support. Polydopamine nonspecifically adheres to virtually any surface with which it comes into contact. The deposition process occurs by dissolving dopamine in an alkaline water solution (e.g., from a pH of about 8 to a pH of 14) and immersing a membrane into the solution for a certain period of time (e.g., 1 minute to multiple days). The skilled artisan will appreciate that the length of time of exposure of the membrane to the dopamine solution may be varied to change the amount of dopamine (and therefore polydopamine) deposited on the membrane surface. For example, one can use a dopamine solution concentration of 2 mg of dopamine per ml of tris(hydroxymethyl)aminomethane (TRIS) aqueous buffer (pH=8-10). The skilled artisan will appreciate that the dopamine concentration can be varied, as can the buffer solution used and that the dopamine can be applied from an alkaline aqueous solution with no buffer if desired, to vary the amount of dopamine (and therefore polydopamine) deposited onto the membrane.

In addition to being a polydopamine layer deposited onto the membrane or a membrane composition having polydopamine, the present invention includes layers and composition having dopamine/polydopamine as an additive. When the dopamine/polydopamine is in the form of an additive, the actual dopamine/polydopamine concentration will be a percentage of the total concentration and may be from 0.001 to 50 percent. When the percentage of dopamine/polydopamine is above 50 percent, dopamine/polydopamine will be considered the polymer and any additional compositions will be considered as the additive. For example, the dopamine/polydopamine additive concentration may be 0.1, 0.2, 0.3, 0.4, 0.5, 1, 2, 3, 4, 5, 10, 15, 20, 30, 40, to 50 percent. As the percentage listed here are for example it should be understood that the skilled artisan contemplates the use of as an additive for each and every value listed between 0.001 and 50, e.g., 37.45% and 14.96%.

The present inventors recognized that most membranes that undergo a surface modification usually exhibit a significant pure water flux loss, as the modification usually involves adding a polymer layer that remarkably increases a membrane's overall mass transfer resistance. For an example of this loss in water flux upon modifying, the surface of a membrane, the skilled artisan is referred to Ju et al., Journal of Membrane Science, volume 307, pp. 260-267 (2008) which shows a reduction in water permeance through the ultrafiltration membrane from 141 L/(m² h bar) in an unmodified membrane to 36 L/(m² h bar) in a membrane which has been modified with poly(ethylene glycol)-type materials. Polydopamine modified membranes can be simply engineered to lose relatively little pure water flux when compared to uncoated membranes, as the amount of polydopamine deposited on the membrane is very small.

Furthermore, delamination is generally a problem when using a highly hydrophilic polymer coating on a hydrophobic membrane, as the hydrophilic polymer coating will swell in water. The present inventors recognized that the chemical structure of polydopamine (e.g., the dopamine monomer contains two hydroxyl groups) most likely leads to strong physical bonding with membrane supports. These physical bonds insure high polydopamine binding so that delamination of the coating layer does not occur. Physical evidence of this strong binding was observed when a polydopamine modified polysulfone UF membrane was sonicated under extreme acidic conditions (3N HCl) for 5 minutes without visual loss of the polydopamine layer.

The present inventors recognized that polydopamine deposition can be used on a variety of surfaces and allows surface modification to a variety of membranes, regardless of membrane material. Most surface modification techniques used in the art have only been accomplished using one specific type of membrane. Furthermore, the present inventors recognized that the hydrophilicity of polydopamine rivals that of poly(ethylene-glycol)-modified surfaces (as confirmed by contact angle measurements), which have been used extensively as anti-fouling surface modifiers.

The present inventors recognized that in order for sufficient polydopamine to deposit on a membrane surface it takes a significant amount of time since the oxidation reaction to convert dopamine to polydopamine and the deposition are relatively slow processes. For example, the present inventors used samples that had been immersed in a dopamine solution for 60 minutes for use in studies of reducing biofilm formation and anti-fouling. Although this is not exceedingly long, for industrial practicality, shorter or longer immersion times may be deemed optimal. The present inventors recognized that depending on many factors, the membrane immersion in the dopamine solution may be varied from 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 50, 60, 120 or more than 120 minutes depending on factors such as solution pH, dopamine concentration, substrate material temperature, and so forth.

The present inventors recognized that the polydopamine structure is also of interest in oxidative (alkaline) environments, as properly conjugated molecules will covalently bond to it and allow the use of the polydopamine as an intermediate layer between a hydrophobic membrane and a hydrophilic coating. The polydopamine layer improves adhesion to the membrane support, allowing long-term membrane operation. Furthermore, the hydrophilicity of the polydopamine structure increases the wettability of polydopamine coated hydrophobic membranes and reduces defects in a hydrophilic coating layer. A membrane coating layer further reduces fouling by not allowing biofilm formation on the porous structure of the underlying membrane.

The present invention provides a polydopamine deposition layer over a substrate layer and allows the substrate to be a variety of substances and materials. The polydopamine deposition layer of the present invention provides a high hydrophilicity and is suited to alleviate biofilm formation when used to modify water purification membrane surfaces.

Polydopamine, a hydrophilic polymer, can deposit on virtually any surface with which it comes into contact. Therefore, it has potential to be widely used as an effective anti-fouling coating layer in many membrane water purification applications. The present inventors recognized that a polydopamine layer resists fouling when deposited on reverse osmosis (RO) polyamide, nanofiltration (NF) polyamide, and ultrafiltration (UF) polysulfone membranes. However, the skilled artisan will appreciate that if dopamine can positively influence the fouling characteristics of these membranes, it should also positively influence the fouling characteristics of other membranes and filter media, such as microfiltration (MF) membranes.

In some instances, the flux of the polydopamine coated membrane is the same as the uncoated membrane and, therefore, exhibits 100% flux when compared to the uncoated membrane. The polydopamine modification can, in some instances with hydrophobic microfiltration membranes or large pore ultrafiltration membranes, impart added wettability to the pore structure, which, when coupled with a negligible decrease in its pore size, leads to an effective increase in pure water flux over that of the unmodified membrane. The polydopamine coated membrane may have a high flux given the presence of a coating on the membrane and range between 150% and 0% flux when compared to the flux of an unmodified membrane. Common high flux values for the polydopamine modified membrane are about 125, 110, 99, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, and 5% of the flux when compared to a unmodified membrane. However, the skilled artisan will recognize that the percentages are estimates and may vary by ±5 percent. In addition, the polydopamine, the membrane, or both may be further modified by the addition of one or more of the following: nanometals, nanoparticles, halogens, hydroxyl groups, lower alkyl groups, lower alkoxy groups, monocyclic aryl, lower acyl groups, one or more functional groups chosen from ROOH, ROSH, RSSH, OH, SO₃H, SO₃R, SO₄R, COOH, NH₂, NHR, NR₂, CONH₂, and NH—NH₂, wherein R denotes: linear or branched hydrocarbon-based chains, capable of forming at least one carbon-based ring, being saturated or unsaturated; alkylenes, siloxanes, silanes, ethers, polyethers, thioethers, silylenes, silazanes and combinations thereof.

The support membrane used for polydopamine modification may include one or more of the following: poly(methyl methacrylate)s, polystyrenes, polycarbonates, polyimides, epoxy resins, cyclic olefin copolymers, cyclic olefin polymers, acrylate or methacrylate polymers, polyethylene terephthalate, polyphenylene vinylene, polyether ether ketone, poly (N-vinylcarbazole), acrylonitrile-styrene copolymer, or polyetherimide poly(phenylenevinylene), polysulfones, sulfonated polysulfones, copolymers of styrene and acrylonitrile, poly(tetrafluoroethylene), poly(ethylene-co-propylene-co-diene), poly(arylene oxide), polycarbonate, cellulose acetate, piperazine-containing polymers, polyelectrolytes, styrene-containing copolymers, acrylonitrilestyrene copolymers, styrene-butadiene copolymers, styrene-vinylbenzylhalide copolymers, cellulosic polymers, cellulose acetate-butyrate, cellulose propionate, ethyl cellulose, methyl cellulose, nitrocellulose, polyamides, polyimides, aryl polyamides, aryl polyimides, polyethers, poly(arylene oxides), poly(phenylene oxide), poly(xylene oxide), poly(esteramide-diisocyanate), polyurethanes, polyesters (including polyarylates), poly(alkyl methacrylates), poly(acrylates), poly(phenylene terephthalate), polysulfides, poly(ethylene), poly(propylene), poly(butene-1), poly(4-methyl pentene-1), polyvinyls, poly(vinyl chloride), poly(vinyl fluoride), poly(vinylidene chloride), poly(vinylidene fluoride), poly(vinyl alcohol), poly(vinyl esters), poly(vinyl acetate), poly(vinyl propionate), poly(vinyl pyridines), poly(vinyl pyrrolidones), poly(vinyl ethers), poly(vinyl ketones), poly(vinyl aldehydes), poly(vinyl formal), poly(vinyl butyral), poly(vinyl amides), poly(vinyl amines), poly(vinyl urethanes), poly(vinyl ureas), poly(vinyl phosphates), poly(vinyl sulfates), polyallyls; poly(benzobenzimidazole), polyhydrazides, polyoxadiazoles, polytriazoles, poly (benzimidazole), polycarbodiimides, polyphosphazines and combinations thereof.

A membrane coating layer further reduces fouling by not allowing foulants to come into contact with the porous structure of the underlying membrane. The binding of hydrophilic layers to hydrophobic membranes also serves a practical purpose in other membrane applications, including pervaporation and gas separations, in which the swellability of the hydrophilic polymer is an issue.

FIG. 1 is a schematic of the structure of dopamine and the assumed structure of polydopamine. The dopamine self-polymerization reaction changed the color of the solution from transparent red to dark brown in less than one hour and the deposited polydopamine was visible on the membrane surface after only a few minutes of immersion time. This deposited layer was tightly bound to the surface of the membrane, as there was no membrane discoloration even after sonication under 3N HCl for about 5 minutes. In addition, scratching the membrane surface did not visibly remove the deposited layer.

Although the schematic above provides a dopamine and polydopamine structure, the present invention also provides other amine substituted benzenediol compositions may be used. For example, the present invention may use any aromatic dihydroxy group-containing molecule to form a membrane modifying agent. The aromatic molecule may contain 3 to 8 carbons and include one or more hetero atoms, e.g., benzothiazole, benzisoxazole, benzoxazole, indazole, purine, benzimidazole, benzo[c]thiophene, benzothiophene, isoindole, indole, isobenzofuran, benzofuran, naphthalene, naphthalene derivatives, quinoline, quinazoline, cinnoline, isoquinoline and substations and modifications thereof. Furthermore, dopamine or other aromatic dihydroxy and amine-containing molecules could be copolymerized or one member of a multi-monomer composition with a variety of different molecules containing aromatic dihydroxy, amine, or thiol functionality. These polymers can also be used to modify membrane surfaces.

FIG. 2 is a plot of the permeance of UF polysulfone membranes with different polydopamine deposition times. FIG. 2 also presents dopamine deposition on thin, nonporous polysulfone (Udel) films as a function of immersion time (as measured by ellipsometry). Water transport through a polydopamine-modified polysulfone membrane was characterized as a function of membrane immersion time in the dopamine polymerization solution. The water flux decreased with increasing immersion time, as a larger amount of polydopamine was allowed to deposit on the membrane. However, PDOPA forms an extraordinarily thin film at low solution contact time (˜5 nm at 30 m), which leads to small decreases in membrane flux. Therefore, when membranes are immersed for less than 1 hour, they show only a slight decrease in water flux when compared to an unmodified membrane. For example, a membrane with an immersion time of 30 minutes retained approximately 80% of an unmodified membrane pure water flux. This suggests that the membrane's pore structure was generally unaffected by the polydopamine deposition at low immersion times. The polydopamine did not form a defect-free adlayer on the surface of the membrane, but rather deposited conformally on the membrane surface and the membrane pore structure. Therefore, using small-time polydopamine immersions led to a membrane with higher hydrophilicity, as seen with contact angle measurements, without a significant loss of membrane pure water flux. Table 1 shows the correlation between hydrophilicity as seen with contact angle measurements and the PDOPA deposition time on the substrate.

TABLE 1 PDOPA dep. time [h] Contact angle (°) 0 109 ± 5  0.16 49 ± 7 1 49 ± 4 2 58 ± 2 4 47 ± 5 8 47 ± 1 12 53 ± 4 16 55 ± 7

Decane-in-water captive bubble contact angle measurements were used to investigate surface hydrophilicity. Table 1 illustrates decane-in-water captive bubble contact angles for polysulfone membranes subjected to various dopamine deposition times. Because of a spontaneous, fast polydopamine deposition, a dramatic increase in the polysulfone membrane surface hydrophilicity was seen. As presented in the above Table 1, a polysulfone UF membrane contact angle significantly decreased after only 10 minutes (0.16 hours) of dopamine immersion. The contact angle for membranes immersed for larger periods of time indicate that the surface hydrophilicity remained unaffected after the initial polydopamine deposition occurs. A similar increase in surface hydrophilicity was exhibited for other membranes studied, as shown in Table 2. This increase in surface hydrophilicity had a dramatic impact on membrane fouling resistance.

TABLE 2 Contact angle (°) Sample Unmodified PDOPA modified XLE RO 45 ± 3 36 ± 4 NF-90 49 ± 2 40 ± 3 PP MF* 81 + 2 33 ± 5 PTFE MF* 120 ± 6  50 ± 3 PVDF MF* 31 ± 1 31 ± 4 *air-in-water bubbles

In Table 2, the samples include an XLE reverse osmosis membrane (XLE RO), an NF-90 nanofiltration membrane (NF-90), a polypropylene microfiltration membrane (PP MF), a poly(tetrafluoroethylene) microfiltration membrane (PTFE MF), and a poly(vinylidene fluoride) microfiltration membrane (PVDF MF). Air-in-water bubbles were used for the large pore MF membranes, as decane would readily absorb into the membrane structure. At larger immersion times, the dopamine deposition eventually leads to a constriction of the pore structure, therefore reducing membrane flux. This constriction is also of interest (e.g., immersion times>16 hours), as polydopamine is capable of forming a highly hydrogen bonded network, with potentially unique separation properties in areas such as gas separations or water desalting applications or other water purification applications.

FIGS. 3A, 3B, 3C, 3D, 3E, 3F, 3G, and 3H are graphs of membrane fouling studies using either a nonionic oil emulsion (1500 ppm oil-water emulsion (1350 ppm vegetable oil plus 150 ppm DC-193 surfactant), FIGS. 3A-G) or a positively-charged oil emulsion (150 ppm oil-water emulsion (135 ppm decane plus 15 ppm dodecyl trimethyl ammonium bromide (DTAB)), FIG. 3H). NF and RO membranes reject ions, and therefore fouling feed water involving these membranes also contained 2000 ppm NaCl. A 1 hour polydopamine immersion time was chosen as a standard for MF membranes modified in this study; a 45 minute deposition time was used for UF membranes, and a 30 minute deposition time was used for the NF and RO membranes, except in FIG. 3H, where a polydopamine deposition time of 1.5 hours was used. These deposition times ensured that all modified membranes retained at least 80% of their respective unmodified membranes' pure water fluxes and significant changes in membrane surface properties (i.e., contact angle) were observed. PEG grafting to the polydopamine layer was accomplished using a 1 hour grafting time of a 5 kDa amine-terminated PEG.

Regardless of membrane structure or polymer composition, the polydopamine-modified membranes (termed “PDOPA” in these figures) and PEG grafted onto the polydopamine-modified membranes (termed “PDOPA-g-PEG” in these figures) outperformed their unmodified counterparts in these oil-emulsion fouling trials. For example, FIG. 3A, which presents modified and unmodified polysulfone UF membrane fouling, shows that, during most of this study, the polydopamine-modified membrane has a flux more than 2 times higher than the unmodified membrane while exhibiting similar organic rejection after one hour of filtration. PEG grafting to the polydopamine layer results in a slight improvement in flux over the polydopamine-modified membrane. Generally, PEG grafting to MF membranes leads to a considerable improvement in flux over both PDOPA modified membranes and unmodified membranes (as evidenced in FIGS. 3B, F, and G), whereas polydopamine depositions leads to only a slight improvement in flux over unmodified membranes, but a significant increase in organic rejection. In UF membranes (FIGS. 3A and E), PEG grafting to the polydopamine layer does not significantly improve membrane flux over polydopamine deposition alone. However, this may be due to a modest decrease in pure water permeance associated with the PEG grafting. A low initial membrane flux most likely inhibits the flux of the PDOPA-g-PEG modified UF membranes. However, the fouling resistance of both PDOPA-g-PEG and PDOPA modified membranes is significant compared to their unmodified counterparts. RO and NF membranes (FIGS. 3 C and D) exhibit similar fouling trends, with the polydopamine-modified membranes outperformed the unmodified membranes. In both cases, the PDOPA-g-PEG modified membranes have a lower flux throughout the filtration, yet show no indications of fouling (i.e., they exhibit no flux drop through the course the filtration). FIG. 3H also shows the efficacy of polydopamine and PEG grafting to the polydopamine layer on a RO membrane to reduce fouling of a very aggressive, positively-charged decane-DTAB emulsion. RO membranes have a negative surface charge due to an excess of carboxylic moieties as a result of their polymerization chemistry. Therefore, positively-charged foulants are electrostatically attracted to the membrane surface, which leads to dramatic fouling. However, the modifications, in particular the PEG grafting, lead to lower fouling and higher flux throughout the course of the filtration of this positively-charged emulsion.

As mentioned earlier, ions are rejected to a significant degree by NF and RO membranes. Here, salt rejection of unmodified polyamide-based RO and NF membranes is lower than that of their respective PDOPA modified membranes when no organics are present in the feed stream. However, the unmodified RO and NF membranes exhibit slightly higher salt rejection in fouling experiments than PDOPA modified membranes. This is most likely caused by higher amounts of oil adsorption in the unmodified polyamide separating layer. This adsorption leads to a higher mass-transfer resistance, which leads to lower salt permeability in the membrane.

The skilled artisan will recognize that many types of PEG or related structures can be grafted to a dopamine structure given the present invention. For example, many such compounds are taught in U.S. Pat. No. 6,280,853, which is incorporated herein by reference.

FIG. 4 presents the ratio of pure water permeance before (P_(w,o)) and after (P_(w,f)) the non-ionic oil emulsion filtrations presented in FIG. 3 of unmodified, PDOPA modified, and PDOPA-g-PEG modified MF, UF, NF, and RO membranes. Prior to collecting the post-fouled membrane pure water permeance, the membranes were rinsed (to remove any unbound foulants) with pure water. As a reference, a perfectly non-fouling membrane would have an irreversible fouling index (defined here as the ratio of the post-fouled membrane pure water permeance (P_(w,f)) to pre-fouled pure water permeance (P_(w,o))) of 1. Polydopamine greatly enhanced the irreversible fouling index of the membranes. For example, an unmodified polysulfone UF membrane retained only 1% of its pure water permeance after 1 h of oil emulsion fouling, whereas a polydopamine modified UF membrane retained 18% of its initial permeance and a polydopamine with PEG amine (Mw=5,000) grafting modified UF membrane retained 21% of its initial permeance. NF and RO modified membranes exhibited improved irreversible fouling resistance over their unmodified counterparts as well. Grafting PEG amine to the surface of these membranes dramatically enhanced the irreversible fouling resistance of the membranes studied, because the irreversible fouling index of the PDOPA-g-PEG membranes was higher than that of unmodified and PDOPA-modified membranes. These data indicate that polydopamine deposition and polydopamine deposition/PEG grafting on membrane surfaces leads to improved membrane efficiency after a cleansing cycle.

TABLE 3 presents static bovine serum albumin (BSA) adhesion data to various modified and unmodified membranes. All membranes in this study were modified using a 1 h polydopamine deposition time, and a 1 h PEG (Mw=5 kDa, amine terminated) grafting time. Fluorescent BSA static adhesion studies were performed using rhodamine-N-hydroxyl succinimide-tagged BSA, which was synthesized and purified using a common procedure¹. To quantitatively compare the amount of BSA adhered to each membrane, fluorescent intensities of each membrane were measured using a plate reader. Polyamide RO and NF membranes were found to have high fluorescent intensity at the same emission wavelength as fluorescein, so rhodamine tagging was used in this study. Remarkably, 2-3 orders of magnitude decrease in protein adhesion is observed after modification for the UF and MF membranes. Furthermore, PDOPA-g-PEG modified membranes exhibit better resistance to protein adhesion than PDOPA modified membranes. This protein adhesion decrease is consistent with the generally accepted link between membrane hydrophilicity and protein adhesion resistance². Furthermore, PDOPA-g-PEG modified surfaces have shown excellent protein adhesion resistance in other studies, which explains the PDOPA-g-PEG modified membranes' low adhesion characteristics^(3,4). These data clearly show the efficacy of polydopamine deposition and further PEG grafting to reduce protein adhesion to membranes, which is a critical step in eliminating membrane biofouling.

TABLE 3 Membrane Normalized Fluorescent Intensity (I_(n)/I_(PSf)) type Unmodified DOPA modified PEG modified XLE RO 0.22 0.10 0.02 NF-90 1.5 0.79 0.05 PSf UF 100 0.71 0.11 PES UF 56 1.79 0.01 PP MF 97 3.28 0.42 PTFE MF 4.3 0.003 0.05 PVDF MF 64 3.64 0.70

Genetically-modified luminescent Pseudomonas aeruginosa, an opportunistic human pathogen known to form robust and ubiquitous biofilm on a number of surfaces, was used to identify PDOPA and PDOPA-g-PEG biofouling efficacy. FIG. 5 presents relative luminescence of membranes exposed to a solution of Pseudomonas aeruginosa for 1 h. High intensity indicates high bacterial adhesion. The plots show luminescence readings with background luminescence subtracted. Error bars are plus/minus 1 standard error (sample standard deviation divided by the square root of sample size). Significant differences in adhesion are realized for the polypropylene (PP) MF membranes, poly(vinylidene fluoride) (PVDF) MF membranes, poly(ether sulfone) (PES) UF membranes, poly(tetrafluoroethylene) (PTFE) MF membranes, NF-90 nanofiltration membranes, and XLE reverse osmosis membranes. In each case, the adhesion of bacteria is statistically reduced by the dopamine coatings relative to the unmodified membrane. PEG grafting produces a statistical reduction in adhesion over polydopamine-modified membranes in a few membranes (i.e., PVDF MF, XLE RO, and NF-90). The enhanced hydrophilicity provided by polydopamine without introducing electrostatic charge to the membrane surface results, as expected, in decreased levels of bacterial adhesion to six of the seven tested membranes. The reduced adhesion at short times shown in this study should result in slower-growing biofilms at longer times.

Polysulfone ultrafiltration Al support was provided by General Electric Water and was used as the UF membrane in FIG. 2 in this specification. Polysulfone UF (Sepro #: PS-20) and polyethersulfone UF (Sepro #: PES-30) membranes were also purchased from Sepro and used in all fouling studies (FIGS. 4 and 5). Reverse osmosis polyamide membranes (XLE RO) and nanofiltration polyamide membranes (NF-90) were provided by Dow Water Solutions and served as the RO and NF membranes, respectively, described in the examples. Polypropylene (0.1 micron, GE catalog #: M01WP) and poly(tetrafluoroethylene) (0.22 micron, GE catalog #: F02LP) MF membranes were purchased from GE Water and Process Technologies. Poly(vinylidene fluoride) MF (0.22 micron, Millipore Cat. #: GVHP) membranes were purchased from Millipore Corp. Dopamine, Trizma (TRIS), decane, DTAB, bovine serum albumin and sodium hydroxide were purchased from Sigma Aldrich. NHS-rhodamine was purchased from Pierce Biotechnology. Amine terminated PEG (PEG amine) was purchased from JenKem Tech, Allen, Tex. (Mw=5,000). Ultrapure water (18.2 Mohm-cm, <1 ppb TOC) was produced from a Gradient A10/RiOs Millipore water purification system. DC193 nonionic surfactant was purchased from Dow Corning. Wesson vegetable oil was purchased from a local supermarket.

Polydopamine deposition onto membranes was accomplished by soaking a 6 inch×6 inch membrane section in isopropanol for at least 5 minutes. The membrane was then transferred to ultrapure water, where it was immersed for at least 15 minutes with the water being changed 2-3 times to insure removal of the isopropanol. Once the water rinsing was completed, the membrane was taped to a glass plate and a casting ring (e.g., 12-15 cm diameter) was securely fastened to the surface of the membrane. The membrane was rinsed under running ultrapure water before the dopamine solution was added to the glass ring. After membrane preparation, 0.1 gram of dopamine-HCl was added to 50 mL of 10-15 mM TRIS buffer (pH=8.8). The sample was vortexed for 5 seconds. The solution was immediately placed in the casting ring. The solution was stirred using a rocker (e.g., 4 degrees and 50 rpm) or an orbital shaker. The solution gradually changed from slightly transparent red color to dark brown color during the course of the reaction. A visible, brown-colored deposition occurred on the membrane surface. The deposition color became darker as the deposition time increased. Membranes were then rinsed and stored in ultrapure water until their use.

PEG grafting to the polydopamine surface layer was accomplished by immersing polydopamine modified membranes in a 1 mg/mL PEG amine (Mw=5000) in 15 mM TRIS buffer (pH=8.8-9) solution at 50-60° C. for one hour. Amine groups will react with the catechol-like polydopamine structure under alkaline conditions via a Michael addition or Schiff base reaction. The membranes were then rinsed and stored in ultrapure water before use. The present invention further describes three mechanisms for reducing biofouling: attachment of a hydrophilic molecule like PEG; attachment of bactericides like silver/copper ions to the polydopamine, and attachment of furanones to the membrane surface to reduce bacterial proliferation. To reduce biofilm formation, the present invention focuses on tuning pertinent membrane surface properties by attaching long chain hydrophilic or hydrophobic polymers to the polydopamine deposition layer. The surface modifications combined with the polydopamine deposition on the surface will reduce fouling and partially soluble salt scaling and improve membrane fluxes.

The crossflow filtration unit used to test oil fouling in NF and RO membranes was purchased from Separations Systems Technologies (FIG. 6, San Diego, Calif.). This apparatus was equipped with three filtration cells, each with an effective filtration area of 7.8 cm×2.5 cm (19.4 cm²) and a flow channel depth of 3.1 mm. The membranes were tested at a crossflow rate of 3.8 L/min and 10.2 atm transmembrane pressure. The permeate of each membrane was collected in a beaker placed on an electronic balance. The balances were connected to a computer and weight measurements were collected every 60 s by a Labview (National Instruments, Austin, Tex.) software program. Organic rejection was calculated using the following equation:

$R = {\left( {1 - \frac{C_{p}}{C_{f}}} \right) \times 100\%}$

Where R is rejection, C_(p) is the organic concentration in the permeate, and C_(f) is organic concentration in the feed. C_(p) and C_(f) were measured using a Total Organic Carbon Analyzer (TOC5050, Shimadzu Corp., Japan). Salt rejection was also measured using equation 1, with C_(p) and C_(f) being the salt concentrations of the permeate and feed, respectively (NaCl was added to the feed prior to fouling studies to make the total NaCl feed concentration 2000 ppm). The salt concentrations were measured using a conductivity meter (Oakton, Vernon Hills, Ill., USA).

The system used in the NF and RO fouling employed a diaphragm pump (Wanner Hydra Cell, Minneapolis, Minn., USA) whose flow rate and pressure were unstable below approximately 3 atm. Therefore, to test UF and MF membranes at lower pressures, a similar system was built using a peristaltic pump (Cole Parmer, USA). The same cell used in the RO system was used in these experiments; however, the UF and MF system was equipped with only one test cell. The MF membranes were tested at a crossflow rate of 2.0 L/min and 0.3 atm (5 psi) transmembrane pressure. To test the UF membranes, a diaphragm pump head was used on the peristaltic pump motor drive to achieve higher pressures with stable flow rates. The UF membranes were tested at 2.1 atm (30 psi) and 0.8 L/min crossflow rate. Permeate weight measurements were collected every 10 s for these experiments.

A non-ionic oil/water emulsion was prepared by adding 40.5 grams of vegetable oil and 4.5 grams DC193 surfactant (9:1 oil:surfactant ratio) to water to make 3 kilograms of total solution. n-Decane/DTAB emulsions were prepared by adding 4.05 grams n-decane, 0.45 grams DTAB to water to make 3 kilograms of total solution. The mixtures were blended at 20,000 rpm for 3 minutes in a high-speed blender (Waring LBC15, Torrington, Conn.). The mixtures were diluted with pure water to make a total organic concentration of 1,500 ppm for the non-ionic oil/water emulsion or 150 ppm for the n-decane/DTAB emulsion.

Irreversible oil fouling is determined by comparing the pure water permeance of a membrane before and after a fouling experiment. Before a fouling experiment, the pure water flux of a membrane was determined at the same pressure and crossflow rate that the fouling experiment took place (for example, at 2.1 atm and 0.8 L/min for a UF membrane). For NF and RO membranes, saltwater flux and rejection (with no organics present) were determined immediately after the pure water flux (NaCl was added to the feed until the total feed concentration was 2000 ppm). A fouling experiment was then performed on the membranes (for the NF and RO membranes, the fouling experiment time was 24 h, for the UF and MF membranes, a 1 h fouling time was used). After the fouling experiment, the crossflow system was flushed with ultrapure water at least three times, after which time water was allowed to circulate through the system (the rinsing cycle took a total of one hour to complete for the NF and RO membranes and 30 minutes for the UF and MF membranes). The post-fouling pure water flux was recorded after the rinsing cycle.

To test pure water permeability of the polysulfone UF membranes in FIG. 2, cylindrical stirred dead-end cells were used. In this mode of filtration, the whole feed stream is allowed to challenge the membrane, making it ideal for studying pure water permeation. Pure water flux studies were performed for each membrane at three pressures: 10, 20 and 40 psi (0.7, 1.3 and 2.7 atm), respectively. Dead-end cell sizes with effective filtration areas of 11.5 cm² were used.

Protein adhesion experiments were performed using a fluorimetric assay of tagged bovine serum albumin. R-NHS-tagged BSA was used to acquire data in this study, as polyamide membranes were found to have a large fluorescent intensity at approximately the same excitation/emission wavelengths as fluorescein. The fluorescent tagging of BSA was accomplished using a common approach⁵. Briefly, 40 mg BSA was dissolved in 5 mL of ultrapure water, and 8 mg R—NHS was dissolved in 175 μL of dimethyl sulfoxide. 150 μL of the R-NHS solution was added to the BSA solution and incubated at room temperature for 1 h, after which the reaction was quenched by adding 50 μL of glycine buffer. The reaction mixture was purified by eluting through sephadex columns and then dialysis against ultrapure water using Slide-A-Lyzers for 24-48 hours (Thermo Fisher Scientific, Inc. #66380, Rockford, Ill., USA). The final concentration and fluorescent tags per BSA molecule were analyzed using UV spectrophotometry⁵. There were approximately 3.5 rhodamine molecules per BSA molecule. 2.5 cm (1 in.) diameter samples were cut from flat-sheet membranes. The circular samples were placed in dead-end cells (Advantec MFS, #UHP 25, Dublin, Calif., USA) having an effective surface area of 3.5 cm² and washed several times with ultrapure water. R-NHS-tagged BSA solution (0.1 mg/mL in ultrapure water) was then added to the cells. After 1 h, the protein solutions were decanted and the membrane surface was washed gently three times with ultrapure water. The membranes were then air-dried and tested for fluorescent intensity using a plate reader (Tecan Sapphire II, Mannedorf, Switzerland).

Bacterial adhesion to modified and unmodified membranes was performed using an assay of genetically-modified luminescent bacteria. A freezer stock of Pseudomonas aeruginosa (stored at −80° C.) was provided by the Marvin Whiteley laboratory. The bacteria were genetically modified by the Whiteley lab from the PA14 strain of Pseudomonas aeruginosa containing the pQF50 parent plasmid. Plasmids are extra-chromosomal DNA molecules that are expressed by the cell. Plasmids, which occur naturally in bacteria, are also able to replicate independent of the chromosomal DNA. A lux operon (a sequence of five genes) of Photorabdus luminescens is responsible for the light-producing ability of this bacterium. The lux operon from P. luminescens was cloned into the pQF50 plasmid of P. aeruginosa to produce the pQF50-lux plasmid. This alteration allows Pseudomonas aeruginosa to luminesce. Cells are grown from the freezer stock in the presence of carbenicillin antibiotic. The pQF50-lux plasmid contains genes that give the bacteria resistance to the carbenicillin antibiotic. Light production is a very energy-intensive process. If the genes responsible for luminescence are contained on a plasmid, the cell will readily discard the plasmid to avoid the energetic requirements of such. However, if the same plasmid containing the lux operon also provides resistance to an antibiotic in the growth media, the cell will retain the plasmid, thus retaining its luminescent quality.

Culture plates were prepared on LB agar (Miller formulation) that was dissolved in deionized water according to manufacturer instruction and autoclaved. Carbenicillin antibiotic was added to produce a mixture with a carbenicillin concentration of 100 μg/mL. This mixture was poured into sterile petri plates and cooled. The plates were stored at 4° C. Liquid LB media was also prepared according to manufacturer instruction and autoclaved. Again, enough carbenicillin was added to produce a mixture with a carbenicillin concentration of 100 μg/mL.

Cells were grown by streaking a bit of the freezer stock on a culture plate and incubating overnight at 37° C. A single colony was picked from the plate and grown in liquid media (containing 100 μg/mL carbenicillin) overnight at 37° C. with shaking A 0.5 mL aliquot of the liquid culture was diluted with 4.5 mL fresh LB media without antibiotic and grown for about two hours at 37° C. with shaking, until the optical density at 600 nm was in the range of 0.3-0.5. This dilution/growth procedure ensures that the bacteria are in log-phase growth during the experiment for maximum attachment and luminescence. The liquid culture was diluted with more fresh media to an optical density of 0.1, corresponding to 10⁸ cells/mL (a standard cell concentration for bacteriological assays).

Unmodified, PDOPA-modified, and PDOPA-g-PEG-modified 1″-diameter membranes were loaded in dead-end cells. The bacteria suspension was dispensed into the dead-end cells (2 mL) and incubated at 37° C. for one hour. After one hour, the bacteria suspension was removed and the membranes were gently rinsed with about 10 mL deionized water. Four ¼″-diameter samples were cut out of each membrane and loaded into an opaque white 96-well plate. 100 μL fresh LB broth (no antibiotic) was dispensed into each cell to ensure that the bacteria would luminesce during the assay. Luminescence (with no filter) was measured in a BioTek Synergy HT plate reader (BioTek, Winooski, Vt.) running KC4 software. Luminescence of membrane samples with no bacteria was measured and any background was subtracted from the sample luminescence readings. High luminescence indicates high bacterial adhesion.

Although dopamine is discussed here as a membrane modifying agent, multiple embodiments using the functionalized chemistry seen in dopamine could lead to similar anti-biofilm formation membrane coatings. These key functionalities are the catechol-like dihydroxy phenyl group and the amine group, which have been identified in the literature as key elements in a mussel's adhesive plaque. Therefore molecules, or multiple molecules, whose substituents include aromatic dihydroxy groups and amine groups, could be used to modify membrane surfaces. Furthermore, thiol groups have also been shown to react with the catechol-like dihydroxy phenyl group. Therefore, any thiol containing molecule could also be combined with any aromatic dihydroxy group-containing molecule to form a membrane modifying agent. Furthermore, dopamine or other aromatic dihydroxy and amine-containing molecules could be copolymerized with a variety of different molecules containing aromatic dihydroxy, amine, or thiol functionality. These new polymers can also be used to modify membrane surfaces.

Currently, almost all conventional membrane modifications are performed before they are placed in modules. In contrast, the polydopamine treatments and compositions of the present invention have an advantage over other conventional surface modification techniques in that the surface modification can be performed on the membranes after they have been processed into module form. The present invention provides methods and compositions for the modification of conventional water purification membranes purchased in spiral-wound modules, hollow fiber modules, flat sheets or other preformed structures (as described elsewhere). To coat polydopamine and similar adherent polymers to commercial membranes on a large scale, a slightly modified water purification crossflow system can be used. For example, FIG. 7 illustrates an image and schematic of a laboratory-scale crossflow system.

FIG. 6 illustrates a crossflow system 10 having a feed tank 12 connected to membrane cells or modules 14 a, 14 b and 14 c. The crossflow system 10 may also include a flow meter 16, pressure gauge 18, thermometer 20 and balances 22 a, 22 b and 22 c. As a crossflow system schematic 24 it can be seen that the feed tank 12 is kept at a constant temperature and connected to a pump 26 that is connected to a bypass 28, a flow-meter 30 and pressure gauge 32. The pressure gauge 32 is connected to one or more membrane cells 14 a, 14 b and 14 c. Although there are 3 membrane cells/modules illustrated here, the skilled artisan will recognize that this is for simplicity's sake only and the present invention may include numerous membrane cells/modules 14. One or more membrane cells 14 a, 14 b and 14 c allow some of the substance to pass through and be collected 34 a, 34 b and 34 c. Although this is depicted as separate containers the skilled artisan will readily understand that there may be a single or numerous containers. A temperature gauge 36 and a may be fitted to the system. In the crossflow system 10 pictured in FIG. 6, the feed water in the feed tank 12 is pumped through a series of membrane cells 14 at high transmembrane pressure. A portion of the feed water contacts the membrane surface 40 and allows pure water to pass through the membrane 40 and collected 34, while rejecting contaminants. The portion of the feed water that does not pass through the membrane 40 is returned to the feed tank 12 for future filtration.

A schematic of the modified crossflow system is shown in FIG. 7. The modified crossflow system 42 includes a feed tank 12 which contains a dopamine solution 44 and is connected to a pump 26 that is connected to a bypass 28, and a flow-meter 30. Optionally, modified crossflow system 42 may include a filter 46 positioned before membrane cells 14 and membrane module 40. The modified crossflow system 42 may also be connected to a pressure gauge 32, temperature gauge 36 and/or a pressure regulator 48 in any order or combination necessary. In addition, the present invention may include “n” number distributions of a filter 46 positioned before membrane cells 14. “n” may be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10-100, or more than 100 repeats. Although there is only one filter 46 positioned before one membrane cell/module 14 illustrated here, the skilled artisan will recognize that this is for simplicity's sake and the present invention may include numerous membrane cells/module 14. In the crossflow system 10 pictured in FIG. 7, the dopamine solution 44 in the feed tank 12 is pumped using pump 26 through a series of one or more membrane cells/modules 14 at low or high transmembrane pressure. The dopamine solution 44 passes in contact with the membrane surface 40 and allows the dopamine solution 44 to be deposited on the membrane 40. The remaining dopamine solution 44 is returned to the feed tank 12.

One advantage of the present invention is the ease of application of the polydopamine to the membrane surfaces of small and large-scale membrane modules. The approach further allows modification of all wetted membrane module parts regardless of the membrane material. Polydopamine permits the tuning of membrane surface properties for specific applications. A library of compounds is available to covalently attach to the polydopamine layer. The polydopamine deposition method is advantageous over other modifications, because of the non-specific adherence of polydopamine to the membrane surface and modification of all wetted parts of the membrane module. The deposition of polydopamine is achieved by dissolving it in a slightly alkaline water solution (pH 8-10) and circulating the dopamine solution through a menbrane module housing for an extended period of time from about 1 minute to 24 hours, e.g., about 60 minutes.

The current membrane surface modifications in the prior art can have a dramatic pure water flux loss, as the added polymer layer increases the overall mass transfer resistance of the membrane. Polydopamine-coated membranes lose relatively little pure water flux when compared to uncoated membranes, because of the relatively thin polydopamine coating layer. Polydopamine coatings of thickness of about 5 nm are possible on polysulfone membranes, which is a common polymer for ultrafiltration membranes.

For polydopamine to deposit on a membrane surface an oxidation reaction to convert the dopamine to polydopamine needs to occur, this takes a significant amount of time and therefore slows the deposition process. The deposition time of polydopamine can be reduced or optimized by chemical techniques, or by altering the solution pH and dopamine concentration.

Although dopamine is discussed here as a membrane modifying agent, composition and additive, the functionalized chemistry lead to coatings and compositions that reduce biofilm formation. These key functionalities are the catechol-like dihydroxy phenyl group and the amine group, which have been identified in the literature as key elements in a mussel's adhesive plaque. Therefore molecules, or multiple molecules, whose substituents include aromatic dihydroxy groups and amine groups, could be used to modify membrane surfaces. Furthermore, thiol groups have also been shown to react with the catechol-like dihydroxy phenyl group. Therefore, any thiol-containing molecule could also be combined with any aromatic dihydroxy group-containing molecule to form a membrane modifying agent. Furthermore, dopamine or other aromatic dihydroxy and amine-containing molecules could be copolymerized with a variety of different molecules containing aromatic dihydroxy, amine, or thiol functionality. These new polymers can also be used to modify membrane surfaces.

Currently, almost all conventional membrane modifications are performed before they are placed in modules. In contrast, the polydopamine treatments and compositions of the present invention have an advantage over other conventional surface modification techniques in that the surface modification can be performed on the membranes after they have been processed into module form. The present invention provides methods and compositions for the modification of conventional water purification membranes purchased in spiral-wound modules, hollow fiber modules, flat sheets or other preformed structures (as described elsewhere to the artisan). To coat polydopamine and similar adherent polymers to commercial membranes on a large scale, a slightly modified water purification crossflow system can be used, or the membranes can be modified in-place in a large scale water purification plant.

The present invention provides polydopamine treatments for membrane surfaces that have been processed into module forms. For example, to coat spiral-wound membranes, hollow fiber membranes, and flat sheet membranes with polydopamine, a standard purification system (one such crossflow system is described above) may be modified in three ways. First, the permeate side of the membrane module 40 can be initially blocked to eliminate the dopamine solution 44 from being transmitted through the membrane 40. A rubber stopper or a clamp (or other device known to the skilled artisan) (not shown) can be used to block the membrane 40 and is removed after the dopamine treatment. The dopamine solution can also be allowed to permeate through the membrane if so chosen by the artisan by not blocking the permeate during the modification process. Second, an alkaline dopamine solution 44 forms microparticles (not shown) that can impede water flow through the feed-side of membrane modules 40 and therefore could be removed if deemed problematic by the artisan from the feed stream. A particle filter 46 can be placed in-line near the inlet of each membrane module 40 to remove microparticles (not shown) that form during the polydopamine formation. Alternatively, a particle filter 46 may be placed further up-line before the distribution to the inlet of each membrane cell 14. The skilled artisan will readily know that other filters 46 or series of filters (not shown) may be used to accomplish filtration prior to the inlet of each membrane module 14. Therefore, these particles can be removed before the dopamine solution 44 is introduced into the membrane module 14. The particle filter 46 nominal pore diameter may be in between 0.05 microns and 200 microns, with a preferable nominal pore diameter of approximately 5 microns. The particle filter 46 nominal pore diameter need only be sufficient to filter the particles and may use a series of filters 46 with different pore diameters. Third, a small pump 26 can be used in place of the high-powered pump to achieve lower transmembrane pressures. The pump 26 should be capable of operating at low pressures (e.g., 0-500 psig, with a preferable pressure range in between 0-10 psig) and flowrates that keep the residence time of the dopamine solution 44 in each membrane cell 14 between 0.0 seconds and 3 hours, with a preferable residence time between 0.0 seconds and 10 minutes. The small residence time ensures that little microparticle formation is observed in the membrane cell/module 14. Residence time is defined as the total feed-side volume of a membrane cell 14 divided by the volumetric flow rate of the feed-side dopamine solution 44.

In addition, the polymers may be made into a membrane for separations, films, sheets, tubes, rolls, hollow filaments, or fibers objects of a specific shape. In addition, polymers having a porous separation membrane, or substrate, and a coating in occluding contact with the porous separation membrane are also contemplated.

The present invention also provides a method, apparatus and modified crossflow system 42 for the treatment of numerous modules in series. As membrane cells/modules 14 can be added to the modified crossflow system in series, numerous membrane cells/modules 14 (e.g., from 0-100,000,000) can be polydopamine-treated at once. The modified crossflow system can include any number of membrane modules (e.g., 1-10, 10's, 100's, 1000's, 10,000's, 100,000's to more than 100,000,000 membrane modules) connected in series or parallel, series of modules.

In addition, membrane modules can be modified by simply adding an alkaline dopamine solution to either the feed side, permeate side, or both and subsequently sealing the membrane module and mixing by agitating the module (i.e. rolling, shaking, etc.).

Membrane modules may also be modified by use of a clean-in-place (CIP) system. CIP systems permit cleaning of the membrane with pure water or with chemical cleaner in either forward or reverse directions without having to disconnect the membrane module. Typical CIP systems include a pure water or chemical storage/mixing tank and a pump attached to the feed side, permeate side, reject side, or some combination therein. A dopamine solution, as described previously, may be placed in the storage/mixing tank and pumped into the membrane module for modification.

The membrane being modified may be in part or entirely made of one or more polymers. For example, the polymer surface may include Polyethylene (PE); Polypropylene (PP); Polystyrene (PS); Polyethylene terephthalate (PET or PETE); Polyamide (PA); Polysulfone; sulfonated polysulfone or any other polyelectrolyte that is suitable for membrane use; Polyester, Polyvinyl chloride (PVC); Polycarbonate (PC); Acrylonitrile butadiene styrene (ABS); Polyvinylidene chloride (PVDC); Polytetrafluoroethylene (PTFE); Polymethyl methacrylate (PMMA); Polylactic acid (PLA), Polypiperazine, and combinations thereof. In addition, the Polyethylene (PE); Polypropylene (PP); Polystyrene (PS); Polyethylene terephthalate (PET or PETE); Polyamide (PA); Polyester, Polyvinyl chloride (PVC); Polycarbonate (PC); Acrylonitrile butadiene styrene (ABS); Polyvinylidene chloride (PVDC); Polytetrafluoroethylene (PTFE); Polymethyl methacrylate (PMMA); Polylactic acid (PLA) may be modified, substituted or altered by the skilled artisan.

In addition, the polymer may be made from one or more monomers selected from: methyl acrylate, ethyl acrylate, propyl acrylate (all isomers), butyl acrylate (all isomers), 2-ethylhexyl acrylate, isobornyl acrylate, acrylic acid, benzyl acrylate, phenyl acrylate, acrylonitrile, glycidyl acrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate (all isomers), hydroxybutyl acrylate (all isomers), diethylaminoethyl acrylate, triethyleneglycol acrylate, N-tert-butyl acrylamide, N-n-butyl acrylamide, N-methyl-ol acrylamide, N-ethyl-ol acrylamide, trimethoxysilylpropyl acrylate, triethoxysilylpropyl acrylate, tributoxysilylpropyl acrylate, dimethoxymethylsilylpropyl acrylate, diethoxymethylsilylpropyl acrylate, dibutoxymethylsilylpropyl acrylate, diisopropoxymethylsilylpropyl acrylate, dimethoxysilylpropyl acrylate, diethoxysilylpropyl acrylate, dibutoxysilylpropyl acrylate, diisopropoxysilylpropyl acrylate, vinyl acetate, styrene, diethylamino styrene, para-methylstyrene, vinyl benzoic acid, vinyl benzene sulfonic acid, vinyl propionate, vinyl butyrate, vinyl benzoate, vinyl chloride, vinyl fluoride, vinyl bromide, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, methacrylic acid, benzyl methacrylate, phenyl methacrylate, methacrylonitrile, alpha methyl styrene, trimethoxysilylpropyl methacrylate, triethoxysilylpropyl methacrylate, tributoxysilylpropyl methacrylate, dimethoxymethylsilylpropyl methacrylate, diethoxymethyl-silylpropylmethacrylate, dibutoxymethylsilylpropyl methacrylate, diisopropoxymethylsilylpropyl methacrylate, dimethoxysilylpropyl methacrylate, diethoxysilylpropyl methacrylate, dibutoxysilylpropyl methacrylate, diisopropoxysilylpropyl methacrylate, isopropenyl butyrate, isopropenyl acetate, isopropenyl benzoate, isopropenyl chloride, isopropenyl fluoride, isopropenyl bromideitaconic aciditaconic anhydridedimethyl itaconate, methyl itaconate N-tert-butyl methacrylamide, N-n-butyl methacrylamide, N-methyl-ol methacrylamide, N-ethyl-ol methacrylamide, isopropenylbenzoic acid, diethylamino alphamethylstyrene, para-methyl-alpha-methylstyrene, diisopropenylbenzene, isopropenylbenzene sulfonic acid, methyl 2-hydroxymethylacrylate, ethyl 2-hydroxymethylacrylate, propyl 2-hydroxymethylacrylate, butyl 2-hydroxymethylacrylate, 2-ethylhexyl 2-hydroxymethylacrylate, isobornyl 2-hydroxymethylacrylate, and dimethyl Meta-Isopropenylbenzyl Isocyanate. In some embodiments, the polymer may be inpart or entirely made from poly(1-phenyl-2-[p-trimethylsilylphenyl]acetylene, poly(1-trimethylsilyl-1-propyne), poly(ethylene octene), crosslinked poly(ethylene oxide), and 1,2-polybutadiene.

The polymers of the present invention may be modified and/or substituted with one or more halogens, hydroxyl groups, lower alkyl groups, lower alkoxy groups, monocyclic aryl, lower acyl groups and combinations thereof. Furthermore, one or more functional groups for the polymer may be chosen from ROOH, ROSH, RSSH, OH, SO₃H, SO₃R, SO₄R, COOH, NH₂, NHR, NR₂, CONH₂, and NH—NH₂, wherein R denotes, e.g., linear or branched hydrocarbon-based chains, capable of forming at least one carbon-based ring, being saturated or unsaturated; alkylenes, siloxanes, silanes, ethers, polyethers, thioethers, silylenes, and silazanes.

The polymers may include rubbery polymers, stiff chain polymers, glassy polymers and combinations thereof including: poly(1-phenyl-2-[p-trimethylsilylphenyl]acetylene (hereafter referred to as “PTMSDPA”) and poly(1-trimethylsilyl-1-propyne) (hereafter referred to as “PTMSP”) and elastomeric and rubbery polymers including poly(ethylene octene). Other polymers suitable for the present invention can be substituted or unsubstituted polymers and may include polysulfone, copolymer of styrene and acrylonitrile poly(arylene oxide), polycarbonate, and cellulose acetate, polysulfones; poly(styrenes), including styrene-containing copolymers such as acrylonitrilestyrene copolymers, styrene-butadiene copolymers and styrene-vinylbenzylhalide copolymers; polycarbonates; cellulosic polymers, such as cellulose acetate-butyrate, cellulose propionate, ethyl cellulose, methyl cellulose, nitrocellulose, etc.; polyamides and polyimides, including aryl polyamides and aryl polyimides; polyethers; poly(arylene oxides) such as poly(phenylene oxide) and poly(xylene oxide); poly(esteramide-diisocyanate); polyurethanes; polyesters (including polyarylates), such as poly(ethylene terephthalate), poly(alkyl methacrylates), poly(acrylates), poly(phenylene terephthalate), etc.; polysulfides; polymers from monomers having alpha-olefinic unsaturation other than mentioned above such as poly (ethylene), poly(propylene), poly(butene-1), poly(4-methyl pentene-1), polyvinyls, e.g., poly(vinyl chloride), poly(vinyl fluoride), poly(vinylidene chloride), poly(vinylidene fluoride), poly(vinyl alcohol), poly(vinyl esters) such as poly(vinyl acetate) and poly(vinyl propionate), poly(vinyl pyridines), poly(vinyl pyrrolidones), poly(vinyl ethers), poly(vinyl ketones), poly(vinyl aldehydes) such as poly(vinyl formal) and poly(vinyl butyral), poly(vinyl amides), poly(vinyl amines), poly(vinyl urethanes), poly(vinyl ureas), poly(vinyl phosphates), and poly(vinyl sulfates); polyallyls; poly(benzobenzimidazole); polyhydrazides; polyoxadiazoles; polytriazoles; poly (benzimidazole); polycarbodiimides; polyphosphazines; etc., and interpolymers, including block interpolymers having repeating units from the above such as terpolymers of acrylonitrile-vinyl bromide-sodium salt of para-sulfophenylmethallyl ethers; and grafts and blends having any of the foregoing. Substituents providing substituted polymers include halogens such as fluorine, chlorine and bromine; hydroxyl groups; lower alkyl groups; lower alkoxy groups; monocyclic aryl; lower acyl groups and the like.

The present invention includes the use of phenethylamine and modified and substituted phenethylamine monomers. The present invention provides the polymerization of various monomers, polymers and/or co-monomer combinations. For example, monomers may include a single monomer or a combination of 2 or more monomers including phenethylamine, 3-trifluoromethylphenethylamine, 2-chlorophenethylamine, 3-chlorophenethylamine, 4-chlorophenethylamine, 2,4-dichlorophenethylamine, 3-bromophenethylamine, 4-iodophenethylamine, 3-hydroxyphenethylamine, 4-hydroxyphenethylamine, 2,4-dihydroxyphenethylamine, 2-methylphenethylamine, 3-methylphenethylamine, 4-methylphenethylamine, 2,4-dimethylphenethylamine, 2,4,6-trimethylphenethylamine, 3-ethylphenethylamine, 4-ethylphenethylamine, 4-hexylphenethylamine, 3-nitrophenethylamine, 2-aminophenethylamine, 4-aminophenethylamine, 2,4-diaminophenethylamine, 2-methoxyphenethylamine, 3-methoxyphenethylamine, 4-methoxyphenethylamine, 2,4-dimethoxyphenethylamine, 2,4,6-trimethoxyphenethylamine, 3,4-dimethoxyphenethylamine, 2-ethoxyphenethylamine, 3-ethoxyphenethylamine, 4-ethoxyphenethylamine, 3-propoxyphenethylamine, 4-butoxyphenethylamine, 4-t-butoxyphenethylamine, 3-methoxymethylphenethylamine, 4-methoxymethylphenethylamine, 3-(2-methoxyethyl)phenethylamine, 4-(2-methoxyethyl)phenethylamine, 4-(2-hydroxyethyl)phenethylamine, 4-(3-hydroxypropyl)phenethylamine, 4-(2-hydroxyethoxy)phenethylamine, 4-phenylphenethylamine, 4-(2-chlorophenyl)phenethylamine, 4-(2-aminophenyl)phenethylamine, 3-(2,4,6-trimethylphenyl)phenethylamine, 4-phenoxyphenethylamine, 4-(3-chlorophenoxy)phenethylamine, 4-(4-aminophenoxy)phenethylamine, 3-benzylphenethylamine, 4-phenethylphenethylamine, 3-acetylphenethylamine, 4-acetylphenethylamine, 4-(2-phenoxyethyl)phenethylamine, and 3-benzyloxyphenethylamine for phenethylamine, 4-fluorophenethylamine, 3-hydroxyphenethylamine, 2,5-dihydroxyphenethylamine, 2-methylphenethylamine, 3-methylphenethylamine, 4-methylphenethylamine, 2,4-dimethylphenethylamine, 2,4,6-trimethylphenethylamine, 3-ethylphenethylamine, 4-ethylphenethylamine, 4-hexylphenethylamine, 3-nitrophenethylamine, 2-aminophenethylamine, 4-aminophenethylamine, 2,4-diaminophenethylamine, 2-methoxyphenethylamine, 2,5-dimethoxyphenethylamine, 2,3-dimethoxyphenethylamine, 3,5-dimethoxyphenethylamine, 3,4,5-trimethoxyphenethylamine, 3-methoxyphenethylamine, 4-methoxyphenethylamine, 2,4-dimethoxyphenethylamine, 2,4,6-trimethoxyphenethylamine, 3,4-dimethoxyphenethylamine, 2-ethoxyphenethylamine, 3-ethoxyphenethylamine, 4-ethoxyphenethylamine, 3-propoxyphenethylamine, 4-butoxyphenethylamine, 4-t-butoxyphenethylamine, 3-methoxymethylphenethylamine, 4-methoxymethylphenethylamine, 3-methoxyethylphenethylamine, 4-methoxyethylphenethylamine, 4-hydroxyethylphenethylamine, 4-hydroxypropylphenethylamine, 4-hydroxyethoxyphenethylamine, 4-phenylphenethylamine, 4-(2-chlorophenyl)phenethylamine, 4-(2-aminophenyl)phenethylamine, 3-(2,4,6-trimethylphenyl)phenethylamine, 4-phenoxyphenethylamine, 4-(3-chlorophenoxy)phenethylamine, 3,4-methylenedioxyphenethylamine, 6-methoxy-3,4-methylenedioxyphenethylamine, 2-methoxy-3,4-methylenedioxyphenethylamine, 4,5-methylenedioxyphenethylamine, 3-methoxy-4,5-methylenedioxyphenethylamine, 4-(4-aminophenoxy)phenethylamine, 3-benzylphenethylamine, 4-phenethylphenethylamine, 3-acetylphenethylamine, 4-acetylphenethylamine, 4-(2-phenoxyethyl)phenethylamine, and 3-benzyloxyphenethylamine for 4-hydroxyphenethylamine, and substitution and modifications thereof.

Other examples include β-Phenylethylamine (2-Phenylethylamine), Phenethylamine, 4-hydroxy-phenethylamine, 3,4-dihydroxy-phenethylamine, β,3,4-trihydroxy-N-methylphenethylamine, β,3,4-trihydroxyphenethylamine, β,3-dihydroxy-N-methylphenethylamine, 2,4,5-trihydroxyphenethylamine, β,4-dihydroxy-3-hydroxymethyl-N-tert-butyl-phenethylamine, α-methyl-3-acetylphenethylamine, β-ketoamphetamine, N-methyl-β-ketoamphetamine, 3-chloro-N-tert-butyl-β-ketoamphetamine, 3-trifluoromethyl-N-ethyl-amphetamine, 3,4,5-trimethoxyphenethylamine, 3,4-methylenedioxyamphetamine, 3,4-methylenedioxy-N-methylamphetamine, 3,4-methylenedioxy-N-methyl-β-ketoamphetamine, 2,5-dimethoxy-4-methylamphetamine, 2,5-dimethoxy-4-bromoamphetamine, 2,5-dimethoxy-4-nitroamphetamine, 2,5-dimethoxy-4-bromophenethylamine, 2,5-dimethoxy-4-chlorophenethylamine, 2,5-dimethoxy-4-iodoamphetamine, 2,5-dimethoxy-4-iodophenethylamine, 2,5-dimethoxy-4-methylphenethylamine, 2,5-dimethoxy-4-ethylphenethylamine, 2,5-dimethoxy-4-fluorophenethylamine, 2,5-dimethoxy-4-nitrophenethylamine, 2,5-dimethoxy-4-ethylthio-phenethylamine, 2,5-dimethoxy-4-isopropylthio-phenethylamine, 2,5-dimethoxy-4-propylthio-phenethylamine, 2,5-dimethoxy-4-cyclopropylmethylthio-phenethylamine, 5-dimethoxy-4-tert-butylthio-phenethylamine, and 2,5-dimethoxy-4-(2-fluoroethylthio)-phenethylamine. Tyramine, Dopamine, Epinephrine (Adrenaline), norepinephrine (Noradrenaline), Phenylephrine, 6-Hydroxydopamine, Salbutamol, Acetylamphetamine, Cathinone, Methcathinone, Bupropion, Fenfluramine, Mescaline, MDA, MDMA, MDMC, DOM, DOB, DON, 2C-B, 2C-C, DOI, 2C-I, 2C-D, 2C-E, 2C-F, 2C-N, 2C-T-2, 2C-T-4, 2C-T-7, 2C-T-8, 2C-T-9, and 2C-T-21.

The material of the present invention can be subjected to extrusion, injection molding, hot pressing, coating, painting, laminating, and solvent casting, mixtures and combinations thereof and formed into a bead, a film, a tube, a sheet, a thread, a suture, a gauze, a bandage, an adhesive bandage, a vessel, a container, a cistern, a filter, a membrane, a coating, a paint and combinations thereof.

In addition, the polymers, monomers or copolymer may be modified by the addition or substitution of one or more of the following groups: lower alkyl, alkenyl, amino, aryl, alkylaryl, halogen, halo, haloalkyl, phosphoryl or combination thereof. In addition, the modification may be similarly modified with one or more lower alkyl, alkenyl, amino, aryl, alkylaryl, halogen, halo, haloalkyl, phosphoryl or combination thereof.

In addition, the polymers, monomers or copolymer may include monomers that are hydrophilic and/or hydrophobic and may be cross-linked to form polymer films and/or membranes. The skilled artisan will recognize that by varying the degree of cross-linking of the polymers, the polymers can have very high concentrations of ionic groups (i.e., sulfonic acid) without a high water uptake. In addition, the present invention may include sulfonated polymer structures and substrates. For example, current sulfonated polymer membranes for reverse osmosis applications display stability over a pH range of about 4 to about 11, with a high water flux and high chlorine tolerance.

In addition, the polymers may be made into a membrane for separations, films, sheets, tubes, rolls, hollow filaments, or fibers objects of a specific shape. In addition, polymers having a porous separation membrane, or substrate, and a coating in occluding contact with the porous separation membrane are also contemplated.

It is contemplated that any embodiment discussed in this specification can be implemented with respect to any method, kit, reagent, or composition of the invention, and vice versa. Furthermore, compositions of the invention can be used to achieve methods of the invention. The present invention may be made mixed with a material prior, during or after material or article formation and provide anti-biofilm, thermal and photo stabilizing function. The material of the present invention can be subjected to extrusion, injection molding, hot pressing, coating, painting, laminating, and solvent casting, mixtures and combinations thereof and formed into a bead, a film, a tube, a sheet, a thread, a suture, a gauze, a bandage, an adhesive bandage, a vessel, a container, a cistern, a filter, a membrane, a coating, a paint and combinations thereof.

The present invention aims to reduce fouling, scaling, and biofilm formation in conventional polymeric membranes by a novel technique of polymer deposition. The invention describes polydopamine, which is highly hydrophilic and can be deposited onto virtually any surface with which it comes into contact. Polydopamine adheres strongly to the surface, and can covalently link to properly conjugated molecules thereby reducing biofilm formation. Furthermore, polydopamine can react with metal ions, thereby forming metallic particles on the membrane surface via an electronless metallization mechanism.

Polydopamine is a hydrophilic polymer and can deposit on virtually any surface with which it comes into contact. Thus, it can be used as an effective anti-fouling/scaling coating layer in many membrane water purification applications, including wastewater treatment, beverage clarification, oil and natural gas produced water treatment, and desalination. Furthermore, polydopamine's reactive functionalities provide an effective means to graft other non-fouling/scaling molecules on membrane surfaces.

It is contemplated that any embodiment discussed in this specification can be implemented with respect to any method, kit, reagent, or composition of the invention, and vice versa. Furthermore, compositions of the invention can be used to achieve methods of the invention.

It will be understood that particular embodiments described herein are shown by way of illustration and not as limitations of the invention. The principal features of this invention can be employed in various embodiments without departing from the scope of the invention. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, numerous equivalents to the specific procedures described herein. Such equivalents are considered to be within the scope of this invention and are covered by the claims.

All publications and patent applications mentioned in the specification are indicative of the level of skill of those skilled in the art to which this invention pertains. All publications and patent applications are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.

The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and/or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.” The use of the term “or” in the claims is used to mean “and/or” unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and/or.” Throughout this application, the term “about” is used to indicate that a value includes the inherent variation of error for the device, the method being employed to determine the value, or the variation that exists among the study subjects.

The term “or combinations thereof” as used herein refers to all permutations and combinations of the listed items preceding the term. For example, “A, B, C, or combinations thereof” is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, MB, BBC, AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context.

All of the compositions and/or methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and/or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.

REFERENCES

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1. A method of depositing a coating material to reduce or prevent biofilm formation on a surface comprising the steps of: adding a dopamine coating material to a liquid solvent to form a solution mixture; adjusting a pH of the solution mixture to 8, 9, or 10; dissolving the dopamine coating material in the liquid solvent; and contacting the solution mixture with one or more surfaces to form a dopamine coating on the surface to reduce biofilm formation.
 2. The method of claim 1, wherein the contacting occurs by circulating the solution mixture for at least 30 minutes to deposit the coating material on the surface.
 3. The method of claim 1, wherein the dopamine coating is polydopamine.
 4. The method of claim 1, wherein the dopamine coating material further comprises one or more polar molecules, one or more polar hydrophilic molecules, one or more molecules comprising at least one polar group or combinations thereof.
 5. The method of claim 1, wherein the dopamine coating material further comprises one or more polymers, one or more polar sugars, one or more polar salts, one or more polar organic molecules, one or more polar —OH containing molecules, one or more polar —NH₂ containing molecules, one or more polar O containing molecules or combinations thereof.
 6. The method of claim 1, wherein the surface comprises a membrane surface, a bead, a film, a tube, a sheet, a thread, a suture, a gauze, a bandage, an adhesive bandage, a vessel, a container, a cistern, a filter, a membrane, a coating, a paint, a solution, a polymer and combinations thereof.
 7. The method of claim 1, wherein the molecule attached to the coated surface comprises one or more hydrophilic or hydrophobic polymers or combinations thereof.
 8. The method of claim 1, wherein the dopamine coating comprises molecule polyethylene glycol attached to the dopamine coating.
 9. The method of claim 1, wherein the dopamine coating further comprises silver, zinc, copper, metal ions, alloy ions, nanoparticles, metal nanoparticles, inorganic molecules or combinations thereof.
 10. A method of decreasing biofilm formation on a membrane comprising the steps of: depositing a dopamine composition on a membrane to form a polydopamine coated membrane, wherein the polydopamine coated membrane has a higher water flux, an increased membrane surface hydrophilicity and a reduced biofilm formation than an unmodified membrane.
 11. The method of claim 10, wherein the pure water flux of the polydopamine coated membrane comprises between 0 and 99% of the flux of the unmodified membrane.
 12. The method of claim 10, wherein the polydopamine coated membrane comprises between 0 and 50% polydopamine.
 13. The method of claim 10, wherein the dopamine composition comprises one or more substitutions selected from the addition of halogens, hydroxyl groups, lower alkyl groups, lower alkoxy groups, monocyclic aryl, lower acyl groups or combinations thereof.
 14. The method of claim 10, wherein the membrane comprises a RO membrane, a UF membrane, a NF membrane or a combination thereof.
 15. The method of claim 10, wherein the polydopamine coated membrane comprises one or more of the following polymethylmethacrylates, polystyrenes, polycarbonates, polyimides, epoxy resins, cyclic olefin copolymers, cyclic olefin polymers, acrylate polymers, polyethylene teraphthalate, polyphenylene vinylene, polyether ether ketone, poly (N-vinylcarbazole), acrylonitrile-styrene copolymer, or polyetherimide poly(phenylenevinylene).
 16. The method of claim 10, wherein the dopamine comprises one or more functional groups selected from ROOH, ROSH, RSSH, OH, SO₃H, SO₃R, SO₄R, COOH, NH₂, NHR, NR₂, CONH₂, and NH—NH₂, wherein R denotes: linear or branched hydrocarbon-based chains, capable of forming at least one carbon-based ring, being saturated or unsaturated.
 17. The method of claim 10, wherein the dopamine comprises one or more functional groups selected from alkylenes, siloxanes, silanes, ethers, polyethers, thioethers, silylenes, and silazanes.
 18. The method of claim 10, wherein the polydopamine coated membrane comprises one or more polysulfone, copolymer of styrene and acrylonitrile poly(arylene oxide), polycarbonate, cellulose acetate, polysulfones; poly(styrenes), styrene-containing copolymers, acrylonitrilestyrene copolymers, styrene-butadiene copolymers, styrene-vinylbenzylhalide copolymers; polycarbonates; cellulosic polymers, cellulose acetate-butyrate, cellulose propionate, ethyl cellulose, methyl cellulose, nitrocellulose, polyamides, polyimides, aryl polyamides, aryl polyimides, polyethers, poly(arylene oxides), poly(phenylene oxide), poly(xylene oxide); poly(esteramide-diisocyanate), polyurethanes, polyesters (including polyarylates), poly(ethylene terephthalate), poly(alkyl methacrylates), poly(acrylates), poly(phenylene terephthalate), polysulfides, poly (ethylene), poly(propylene), poly(butene-1), poly(4-methyl pentene-1), polyvinyls, poly(vinyl chloride), poly(vinyl fluoride), poly(vinylidene chloride), poly(vinylidene fluoride), poly(vinyl alcohol), poly(vinyl esters), poly(vinyl acetate), poly(vinyl propionate), poly(vinyl pyridines), poly(vinyl pyrrolidones), poly(vinyl ethers), poly(vinyl ketones), poly(vinyl aldehydes), poly(vinyl formal), poly(vinyl butyral), poly(vinyl amides), poly(vinyl amines), poly(vinyl urethanes), poly(vinyl ureas), poly(vinyl phosphates), poly(vinyl sulfates), polyallyls; poly(benzobenzimidazole), polyhydrazides, polyoxadiazoles, polytriazoles, poly (benzimidazole), polycarbodiimides, polyphosphazines and combinations thereof.
 19. The method of claim 10, further comprising the step of applying one or more second coatings to the polydopamine coated membrane.
 20. A liquid separation apparatus having reduced biofilm formation comprising: a purification membrane; a polydopamine layer deposited on the purification membrane to form a polydopamine coated membrane to reduce the formation of a biofilm, wherein the polydopamine layer increases the hydrophilicity of the purification membrane and the polydopamine coated membrane has a high water flux; and one or more containers positioned on different sides of the polydopamine coated membrane to contain the separated liquid.
 21. A polydopamine coated purification membrane system for modification of conventional purification membranes to reduce biofilm formation comprising: a dopamine solution to reduce biofilm formation disposed in a feed tank; a pump connected to the feed tank to move the dopamine solution to provide a high transmembrane pressure; a membrane inlet connection to connected to the pump to a membrane to allows the dopamine solution to be deposited on the membrane; and a membrane outlet connection to connect the membrane to the feed tank to return the dopamine solution to the feed tank. 